The present invention relates to an ink jet head which ejects ink toward a recording medium in response to driving signals, and an ink jet apparatus which records characters images, pictures images. and/or the like, on the recording medium by employing the ink jet head. It also relates to an ink jet recording method for recording images with gradation by driving a plurality of heat generating resistors.
The ink jet apparatus does not generate noise, can record at a high speed, and can easily record color images; therefore, it has come to be widely used as a means for recording images on a recording medium such as a sheet of paper, in various apparatuses, for example, a word processor, a facsimile apparatus, a copying apparatus, or a printer.
The ink jet head is mounted in an ink jet apparatus, as a member which records character images, picture images and/or the like, on the recording medium by ejecting ink from the ink jet portions in response to driving signal input from the ink jet apparatus. More specifically, the ink jet head ejects ink using the thermal energy generated in response to the driving signals from the ink jet apparatus.
FIG. 8 is a schematic perspective view of an ink Jet head, and FIG. 9 is a schematic section of the same ink jet head.
A reference numeral 40 designates an ejection orifice from which the ink is ejected; 41, a first substrate; 41a, a heat generating resistor disposed on the first substrate 41 in order to generate a bubble in the ink by heating the ink; 42, a second substrate; 42a, an ink path; 42b, an ink chamber; and 42c designates an ink supply port.
As is evident from the drawing, the first substrate 41 and the second substrate 42 are joined to form the ink path 42a and the ink chamber 42b. The ink is.supplied through the ink supply port 42c, and is delivered to the ink chamber 42b, and then to the ink path 42a. The heat generating resistor 41a provided within the ink path 42a generates heat in response to the driving signals sent from the driving signal supplying means of the ink jet apparatus. The heat generates a bubble in the ink within the ink path, and as the bubble develops, the ink within the ink path 42a is ejected toward the recording medium from the ejection orifice 40.
Incidentally, as the ink jet apparatus has recently come to be employed in a printer or the like to output picture images or the like, much higher picture quality has come to be demanded. As for conventional means for improving picture quality, there are methods in which density gradation is controlled by controlling the size of the ink droplet.
According to one such method, which is disclosed in Japanese Laid-Open Patent Application No. 132,259/1980, the density gradation of the ink jet is controlled by changing the amount of the ink ejected per picture element. More specifically, a plurality of heat generating resistors are disposed in a single liquid path, and the driving signals are selectively supplied to each heat generating resistor to change the amount of the ink ejected per picture element. The above publication discloses a structure in which two heat generating resistors are arranged in series in the direction in which the ink is ejected, and another structure which two heat generating resistors are arranged in parallel relative to the direction in which the ink is ejected.
However, the conventional methods have the following problems.
First, the structure in which the plurality of heat generating resistors in the same liquid path are arranged in series in the ink ejecting direction, will be described. When the configuration (area size) of one heat generating resistor is the same as the other, there is a difference in the location of the center of gravity, that is, the heat generating center, of each heat generating resistor, between when only one of the heat generating resistors is driven and when both of them are driven at the same time; therefore, the nozzle length must be extended. This problem can be solved by shortening the length (in the ink ejecting direction) of the heat generating resistor on the ejection orifice side. However, the change in the length of the heat generating resistor requires the change in the voltage to be applied to the heat generating resistor. In other words, when the length of the heat generating resistor on the ejection orifice side is shortened, the voltage to be applied to one heat generating resistor has to be substantially differentiated from the voltage to be applied to the other. As a result, there must be as many power sources as heat generating resistors.
Next, the structure in which the two heat generating resistors in the same flow path are arranged in parallel relative to the ejection direction will be described. When the center of gravity of the heat generating resistor is optimally adjusted to agree with a condition in which only one heat generating resistor is driven, the bubble generating power obtainable when both heat generating resistor are driven at the same time becomes too large, scattering the ink droplets. On the contrary, when the center of gravity of the heat generating resistor is optimally adjusted to agree with a condition in which two heat generating resistors are driven at the same time, the bubble generating power obtainable when the ink is to be ejected by driving only one heat generating resistor is liable to become insufficient to eject the ink as the ink droplet. In other words, when the heat generating resistors are arranged in parallel relative to the liquid ejecting direction, satisfactory picLure qudlity cannot be obtained whether two heat generating resistors are driven at the same time or only one heat generating resistor is driven.
The present invention was made to solve the above described problems related to the conventional methods, and its primary object is to provide an ink jet recording head and ink jet apparatus, which are provided with gradation control functions, being thereby enabled to excel in recording quality, and an ink jet recording method for effecting superior gradation.
The inventors of the present invention disclosed in this patent application made the following discoveries as the result of extensive studies of the problems described above; when the plurality of heat generating resistors within the ink flow path are arranged in parallel relative to the ejection direction, and the location of the center of gravity, that is, the heat generating center, of each heat generating resistor is differentiated from those of the others in the ejecting direction. more specifically, when the center of gravity, that is, the heat generating center, of the heat generating resistor is shifted so that the heat generating resistor which forms a smaller dot when driven alone can be displaced toward the ejection orifice side, the aforementioned problems can be solved.
Thus, the present invention proposes an ink jet head comprising ink ejection outlet for ejecting ink, a plurality of heat generating resistors for generating thermal energy contributable to ejecting the ink, and ink flow path comprising the plurality of the heat generating resistors and being in fluid communication with the ejection outlet, the heat generating resistors generating the thermal energy upon receiving a driving signal, so that a bubble is generated in the ink within the ink flow path to eject the ink through the ink ejection outlet; wherein the plurality of the heat generating resistors are arranged in parallel, relative to the ink ejecting direction, in the ink flow path, and the distances from the heat generating centers of the heat generating resistors to the ejection outlet are different.
Further, the present invention proposes an ink jet apparatus comprising: an ink jet head comprising ink ejection outlet for ejecting ink, a plurality of heat generating resistors for generating thermal energy contributable to ejecting the ink, and ink flow path comprising the plurality of the heat generating resistors and being in fluid communication with the ejection outlet, the heat generating resistors generating the thermal energy upon receiving a driving signal, so that a bubble is generated in the ink within the ink flow path to eject the ink through the ink ejection outlet; and signal supplying means for supplying the driving signal to the ink jet head; wherein the plurality of the heat generating resistors are arranged in parallel, relative to the ink ejecting direction, in the ink flow path, and the distances from the heat generating centers of the heat generating resistors to the ejection outlet are different.
Further, the present invention proposes an ink jet recording method for recording images with gradation using an ink jet head comprising ink ejection outlet for ejecting ink, a plurality of heat generating resistors for generating thermal energy contributable to ejecting the ink, and ink flow path comprising the plurality of the heat generating resistors and being in fluid communication with the ejection outlet, the heat generating resistors generating the thermal energy upon receiving a driving signal, so that a bubble is generated in the ink within the ink flow path to eject the ink through the ink ejection outlet; wherein the plurality of the heat generating resistors are arranged in parallel, relative to the ink ejecting direction, in the ink flow path, and the distances from the heat generating centers of heat generating resistors to the ejection outlet are different; and when the heat generating resistor disposed closest to the ejection outlet, among the plurality of the heat generating resistors, is driven alone, an ink droplet with the smallest volume is ejected.
With the provision of the above described structure, even when a plurality of heat generating resistors with various area sizes are disposed within a single ink flow path, the ink, can be stably ejected in any driving mode; therefore, the amount of the ink to be injected per picture element can be reliably varied, enabling to accomplish high quality gradation.
Further, gradation can be controlled without increasing the number of data pads; without increase in the number of the pads, contact reliability is improved. Therefore, it is possible to provide an ink jet head and an ink jet apparatus, which are capable of accomplishing stable gradation, and thereby realizing superior print quality.
These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.